Device with at least one extension arm or support arm for multi-linked crane shaped extension arms, concrete spreader columns and similar

ABSTRACT

The invention relates to a device with at least one extension arm or support arm for multi-linked crane shaped extension arms, concrete spreader columns and similar, comprising at least one hydraulic differential cylinder for actuating a support arm. The cylinder comprises a hollow piston rod which has a tubular segment and two end pieces arranged on the ends of said segment, whereby at least one of the end pieces is welded on to the segment thereof. The welded joint is machined and the root of the weld is eliminated. At least one of the end pieces comprises a through opening which enables tool access in order to machine the hollow cavity of the hollow piston rod.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the National Phase of International Application No.PCT/EP01/15222, filed in Germany on Dec. 22, 2001 designating the UnitedStates of America, which claims priority to German Patent ApplicationNo. 100 64 365.5, filed on Dec. 22, 2000.

BACKGROUND OF THE INVENTION

The present invention generally relates to a device with at least onesupport arm.

Concrete spreader columns made up of column arms that are linkedtogether by means of articulated joints and, with a view to savingspace, are capable of being folded and subsequently being swung out orextended for operating purposes and make use, especially for the lowestextension and/or support arm or arms, of relatively large differentialhydraulic cylinders. These cylinders are employed as a drive for thelifting, lowering and, where appropriate, for the telescoping of anextension arm. The hydraulic cylinders used for this purpose have strokelengths of up to 2.5 m and over. It is practically self-evident thatthese hydraulic cylinders have to be designed sufficiently large anddimensionally stable to render them capable of coping with the forcesthat come into play when the whole of the column is operated. Moreparticularly, when extending and/or moving the arms. Such multi-linkedcolumn structures involve considerable weight.

In order to reduce this weight, particular attention must be paid tominimizing the masses that have to be moved, not least, by means of thelowest hydraulic cylinder. It is therefore desirable for extension armsof this type to be made as light as possible while still being able tocope with these large forces during operation.

It is thus the task of the invention to further develop a device of thedescribed kind in such a manner as to render possible, given skillfuldesign, a reduction of the weight of the device via the differentialhydraulic cylinders that are to be used as drives for the extensionarms, or support arms, of multi-linked crane-shaped extension arms,concrete spreader columns and the like. It is thus designed with a viewto saving weight.

SUMMARY OF THE INVENTION

The present invention concerns a device with at least one extension armor support arm for crane-shaped extension arms, concrete spreadercolumns, lifting platforms, manipulators and similar multi-linkedworking systems. The invention further concerns a method for theproduction of such a device, especially a hydraulic differentialcylinder used for the device. More particularly, the invention concernsthe construction of a concrete spreader column for a concrete pump, beit mobile or in a fixed position, the column (mast) consisting ofseveral sections that can be folded and possibly telescoped, where theoperation of the column arms is effected especially by means ofhydraulic differential cylinders.

According to the invention, this reduction in weight is accomplished bymeans of the features of the device as set out in claims 1 and 9,whereas the process engineering aspects for the fabrication of such adevice are determined by claim 6.

In accordance with the invention, the hydraulic differential cylindersare already turned into lightweight structures by virtue of the factthat the piston rod is designed as a hollow component. The hollow pistonrod comprises this tubular segment and end pieces arranged at the endsof the tubular segment.

According to the invention, the tubular segment and at least one of theend pieces is welded on. Accessibility for the machining tool is assuredby the fact that at least one of the end pieces is provided with anopening by means of which the cutting tool and possibly a smoothing toolcan be introduced into the interior of the piston rod to carry out thenecessary work there. Of course, the invention can also be applied quitegenerally to hydraulic differential cylinders that are usedindependently of the application cases mentioned hereinabove, though thepreferred field of application is constituted by crane-shaped extensionarms, concrete spreader columns and similar manipulators.

These and other features, advantages, and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Some preferred embodiments of the invention will now be described withreference to the drawing, of which

FIG. 1 shows a cross section through a hydraulic differential cylindersuitable for moving an extension arm or a carrier arm;

FIG. 2 shows a detail of the welded joint of FIG. 1, again as a crosssection;

FIG. 3 shows the cross section of another embodiment of such a hydraulicdifferential cylinder, and

FIGS. 4 and 5 show cross sections with piston rods designed as a singlepiece.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a cross section through an embodiment of a hydraulicdifferential cylinder 1 in accordance with the invention.

The hydraulic cylinder 1 consists of the cylinder tube 3 and the pistonrod 2, which is displaceably arranged within the cylinder tube 3 and isdesigned as a hollow piston rod. The hollow piston rod 2 comprises atubular segment 4 that at its ends is provided with the end piece 5 ofthe side of the piston and the end piece 6 on the other side, the piston11 being attached to the end piece 5 on the piston side by means ofscrew connections 10. The opposite end piece may be either welded on orattached in some other way, possibly by means of a thread or screw.However, the opposite end piece may also be designed as a single piecewith the tubular segment. It is also within the scope of the inventionfor both ends of the piston rod to be welded to appropriate end pieces.

The end piece 6 on the pin-jointed end of the piston rod is providedwith two laterally cantilevered tubular stubs 13, 14 for connecting thepiston rod to a column arm or similar and an opening 8 by means of whichit is possible to access the hollow within the piston rod 2 fromoutside. The cross section of the piston rod wall 9 remains uniformlysmooth and plane over the entire region of the tubular segment 4, andeven the transition to the end pieces 5, 6 is shaped in such a manner asto avoid any stress concentration effects. In particular, the transitionfrom the tubular segment 4 to the piston-side end piece 5, which hereconsists of solid material, is provided with a sufficiently large radiusof curvature to assure that no inadmissible stress concentration effectswill occur.

The hollow piston rod 2 is fabricated from end pieces 5 and 6 andtubular segment 4 by means of welded joints 7. The welded joints 7,which in the illustrated embodiment assume the form of V-joints. TheV-joints are preferably shaped by means of a material-removing finishingprocessing in such a manner as to obtain a smooth, plane, and also flushtransition at the joint between the parts to be joined. In this way, oneavoids the possibility of projecting parts of the welded joint, asillustrated in FIG. 2, contributing to the production of stressconcentration effect. The letter A in FIG. 2 designates thestress-concentration-free remainder of the welded joint after thefinishing processing so that the outer surfaces in the region of thejoint remain flush with the adjacent tube surfaces.

Over and above this, FIG. 3 shows a second embodiment 21 of a hydrauliccylinder in accordance with the invention, in which the hollow pistonrod 22 is provided with a welded-on end piece 26, the welded joint beingindicated by the reference numeral 27. As far as the remainder of thehollow piston rod 22 is concerned, it may be made of solid material andtherefore as a single piece incorporating the end piece 25, which in theillustrated embodiment is provided with a thickened wall. The area ofthe thickening is indicated by 25 a. The reference numeral 25 bindicates a thread applied to the outer jacket surface of the end piece25. A corresponding thread 31 a is provided on the piston 31, which cantherefore be screwed onto the end piece 25. The opening for tool access,which is indicated by 28, makes it possible to gain access to the cavitywithin hollow piston rod 22.

FIGS. 4 and 5 show third and fourth (41, 61 respectively) embodiments ofa hydraulic differential cylinder in which hollow piston rods 42 and 62are fabricated from a single piece of material, preferably a cast blankwhich in the embodiment illustrated by FIG. 4 is machined from the upperend in order to form the hollow within it. In the third embodiment, theinternal wall 55 of end piece 45 at the pin-jointed end and tubularsegment 44 is smoothed by means of material-removing machinery in orderto avoid the creation of stress concentration effects. The transition tothe front face at the end of the hollow space 56 assumes the form ofradius's 57 that avoid stress concentration effects.

The same remarks apply with regard to the fourth embodiment illustratedby FIG. 5, with the sole difference being that, in this case, thematerial-removing processing is effected from the other side, that is tosay, from the bottom end of the piston rod as shown in FIG. 5. Again,radius's 78 and 79 are provided in the transition region to avoid stressconcentration effects. The internal wall 75 is once again smoothed bymeans of material-removing machinery in order to avoid the creation ofstress concentration effects.

When the piston rod is a single piece, it is produced from a cast blankby means of subsequent material-removing machining from one end of thepiston rod to form the hollow within it. For example, a material havinga tensile strength of more than 700 N/mm² may be used so that the pistonrod made therefrom will be capable of being very heavily loaded.

It is advantageous in the dimensioning of this hydraulic cylinder, whichhas to move the mass of a concrete spreader column which lies above it,if stress concentrations in the hydraulic differential cylinders can bereduced to a minimum. As, when the design has to take into account theseconcentrations, this has the general effect of increasing the thicknessof the walls of the hydraulic differential cylinders. This increase inthickness goes hand in hand with a corresponding weight increase.However, if one reduces the stress concentrations that can occur duringoperation, it becomes possible to design the wall of the hydraulicdifferential cylinders with appropriately smaller thicknesses. This canlead to considerable weight advantages, especially when one bears inmind that it is very often necessary to use hydraulic differentialcylinders with stroke lengths of 2.5 meters and over.

In accordance with the invention, this reduction in weight can beobtained by subjecting the regions of the welded joints, especially onthe inside of the tubular segment, to finishing processing in the formof material-removing machining and smoothing.

It is essential for the purposes of the preferred embodiment of theinvention, specifically in connection with the case where the piston rodis constituted by a single piece, that the length of the tubularsegment, the transitions between the segment, and the end pieces shouldremain even, as far as a wall thickness is concerned. Additionally, inthe case of changes in the cross section from the tubular segment to theend pieces, there may be provided a radius of curvature in order toavoid stress concentration effects at that surface, and the surface, asa whole, should be smooth. This makes sure that the stress concentrationeffects will be substantially avoided. The stress concentration factoris thus appropriately minimized and/or eliminated, so that it becomespossible to reduce the wall thickness of the tube by this factor andobtain a corresponding weight minimization and/or weight reduction. Thisweight minimization of the hydraulic differential cylinders naturallyalso has effects on the other components of the structure.

If the interior surface of the hollow piston rod is to be machinedand/or smoothed with a view to reducing these loads associated withstress concentrations, or when producing the interior space of thepiston rod from a previously produced solid casting, it will beadvantageous to provide at least one of end pieces of the hollow pistonrod with an opening by which a machining tool can gain access to theinterior cavity of the piston rod. The opening being necessary formachining tool guidance purposes. Further, it is advantageous to providethis opening at the pin-jointed end of the hollow piston rod becausethis has constructional advantages as compared with an opening situatedat the end on the piston side. This is particularly true when the pistonis attached to the closed end of the piston rod on the piston side byprestressing the screws or by means of a threaded joint.

The lighter the extension arm, the greater will be its useful reach inboth the horizontal and the vertical directions. Although therequirement of a light construction applies basically to all thecomponents of the structure, it applies particularly and above all tothe hydraulic cylinder.

A particularly simple method of obtaining material continuity across ajoint is represented by welding, especially front-face welding of theend pieces to the tubular segment. However, in order to reduce stressconcentration, a smooth surface or finish must be achieved in the regionof the welded joint, where smooth means smooth with regard to thesurface and plane with regard to the cross section of the wall. It willbe advantageous, especially at least in these regions. Therefore, theinterior and/or exterior wall of the hollow piston rod must be subjectedto a material-removing process, especially material-removing machining,where care has to be taken to ensure that this processing will not onlyeliminate abrupt changes in wall thickness, but also to remove thewelding seams to such an extent as to eliminate the root of the weldedseam. This is because welding seams will produce stress concentrationseven when, notwithstanding the complete absence of abrupt changes inwall thickness, the root of the welding seam is still present.

In the manner described hereinabove it is possible

-   -   by smoothing the surface,    -   avoiding abrupt changes in wall thickness and    -   eliminating the roots of the welding seams        to avoid stress concentrations and therefore to design the        components of the hydraulic differential cylinder with a smaller        weight, while yet obtaining the same stability.

In the case of single-piece hollow piston rod in which the hollow withinthe piston rod is produced by subjecting a solid blank tomaterial-removing machining, it will be advantageous to produce theblank by means of known shaping processes. For example forging, casting,rolling or similar due to its simple fabrication.

The foregoing are preferred embodiments of the invention and changes andvariations can be made without departing from the spirit and broaderaspects of the invention, as defined in the appended claims, which areto be interpreted in accordance with the principles of patent law,including the Doctrine of Equivalents.

1. A device with at least one extension arm or support arm formulti-linked extension arms, concrete spreader columns, liftingplatforms, manipulators and the like, comprising: at least one hydraulicdifferential cylinder for operating the arm that is articulated on oneside and can be raised, lowered and/or telescoped by means of thehydraulic differential cylinder; wherein the hydraulic differentialcylinder is provided with a hollow piston rod further comprising atubular segment and two end pieces arranged at the ends of this segmentand designed as a single piece; wherein, with a view to avoiding stressconcentrations, the cross section of the wall of the tubular segmentover the entire length of the tubular segment, and the transitions fromthe tubular segment to the end pieces is made to be substantially smoothand plane; wherein, given jointing that establishes material continuityacross the joint, at least one of the end pieces is welded to thesegment creating a welded joint; wherein the welded joint is made to besubstantially flush with the segment and the end piece joined to it bythe welded joint by means of finishing in the form of material-removingprocessing, especially material-removing machining; wherein further theroot of the welded joint is eliminated by the finishing, and the regionof the welded joint, especially on the internal face of the tubularsegment is smoothed, and at least one of the end pieces is provided withan opening through which a cutting tool can be introduced into in orderto gain access to a space within the hollow piston rod for performingthe said finishing therein.
 2. A device in accordance with claim 1,wherein, with a view to avoiding stress concentrations, the crosssection of the wall of the tubular segment over the entire length of thetubular segment and the transitions from the tubular segment to the endpieces are made to be substantially smooth and plane or with a radius ofcurvature that has practically no adverse effects on the strength.
 3. Adevice in accordance with claim 1, wherein at least one of the internalor the external wall of the hollow piston rod is processed and smoothedby means of material-removing processing, especially material-removingmachining in order to minimize stress concentrations.
 4. A device inaccordance with claim 1, characterized in that at least one jointbetween the tubular segment and the end pieces is a welded joint.
 5. Adevice according to claims 4, wherein the welded joint is a welded jointon the front face.
 6. A device in accordance with claim 1, characterizedin that at least one joint between the tubular segment and the endpieces is constituted by a thread; wherein the wall thickness of thetubular segment is increased in its terminal part.
 7. A device accordingto claim 6, wherein the joint between the tubular segment is constitutedby a screw connection.
 8. A method for the production of a hydraulicdifferential cylinder in accordance with claim 1, comprising: forming ablank with a tubular segment; arranging at least one end piece at oneend of this segment, wherein the internal face of this blank is renderedaccessible for a cutting tool by means of an opening provided in atleast one of the end pieces; smoothing at least the region of the weldedjoint between the end piece, the tubular segment, and inside the tubularsegment, by means of material-removing machining process.
 9. A method inaccordance with claim 8, wherein by means of any desiredmaterial-shaping process; forming a blank with a rod-like segment andtwo end pieces provided at the ends of this segment; forming by means ofmaterial-removing processing, especially material-removing machining, anopening in at least one of the end pieces and a hollow space within therod-like element to produce a hollow piston rod.
 10. A multi-linked,mast-like support arm for concrete spreader columns or the like, whereinthe support arm is provided with one or more hydraulic differentialcylinders in accordance with claim
 1. 11. A device with at least oneextension arm or support arm for multi-linked extension arms, concretespreader columns, lifting platforms, manipulators and the like,comprising: at least one hydraulic differential cylinder for operatingthe arm that is articulated on one side and can be raised, loweredand/or telescoped by means of the hydraulic differential cylinder;wherein the hydraulic differential cylinder is provided with a hollowpiston rod further comprising a tubular segment and two end piecesarranged at the ends of this segment or joined to each other in such away as to obtain material continuity across the joint; wherein, with aview to avoiding stress concentrations, the cross section of the wall ofthe tubular segment over the entire length of the tubular segment, andthe transitions from the tubular segment to the end pieces is made to besubstantially smooth and plane; wherein, given jointing that establishesmaterial continuity across the joint, at least one of the end pieces iswelded to the segment creating a welded joint; wherein the welded jointis made to be substantially flush with the segment and the end piecejoined to it by the welded joint by means of finishing in the form ofmaterial-removing processing, especially material-removing machining;wherein further the root of the welded joint is eliminated by thefinishing, and the region of the welded joint, especially on theinternal face of the tubular segment is smoothed, and at least one ofthe end pieces is provided with an opening through which a cutting toolcan be introduced into in order to gain access to a space within thehollow piston rod for performing the said finishing therein.
 12. Adevice according with claim 11, wherein the transitions from the tubularsegment to the end pieces is made with a radius of curvature that haspractically no adverse effects on the strength.
 13. A device accordingwith claim 11, wherein the end piece at the pin-jointed end of thepiston rod is provided with the opening.